1. Field of the Invention
The present invention relates generally to the preparation of alkenyl-substituted intramolecular anhydrides of aliphatic dicarboxylic acids in the presence of catalysts or agents such as 1,3-dibromo-5,5 dialkylhydantion which decrease unwanted by-product formation. More particularly, the invention is directed to a thermal process for preparing polyalkenyl-substituted anhydrides by reacting a polyalkene with an unsaturated aliphatic dicarboxylic acid anhydride in a reaction zone in the presence of a tar and side product suppressing agent, wherein the process comprises the step of adding the anhydride reactant and the tar and side product suppressing agent to the reaction zone in a plurality of stages to suppress formation of tar and other undesired side products.
2. Discussion of the Prior Art
Viscous polyalkenes having number average molecular weights of about 300 to about 3000 and having viscosities in the range of about 4 to about 5500 centistokes at 100.degree. C. are commercially manufactured by Friedel-Crafts polymerization of feeds comprising C.sub.3 to C.sub.5 hydrocarbons and have a wide variety of commercial applications. A principal use is as reactive intermediates in the manufacture of hydrocarbon soluble petroleum additives.
The derivatives of particular interest in the present invention are the polyalkenyl-substituted intramolecular anhydrides of aliphatic dicarboxylic acids. For example, petroleum additive products derived from polybutenyl-substituted saturated aliphatic anhydrides can be added to fuels to inhibit rusting, carburetor deposits, and carburetor icing, corrosion and smoke, and to oils as rust inhibitors, wear inhibitors, dispersants, and VI improvers.
Addition reactions between the viscous polyalkenes and intramolecular anhydrides of unsaturated aliphatic dicarboxylic acid can typically use any one of maleic anhydride, citraconic anhydride, itaconic anhydride, ethyl maleic anhydride, halo (e.g., chloro-) maleic anhydride, glutaconic anhydride, homoesaconic anhydride, and the like according to U.S. Pat. Nos. 2,628,942 and 2,634,256, among others. The addition reactions are, in general, conducted at temperatures in the range of 150.degree. to 300.degree. C. using polyalkene to anhydride molar ratios of reactants in the range of 1.0:1.0-15.
A known problem frequently encountered in the above-mentioned addition reaction is thermal decomposition and polymerization of the unsaturated anhydride reactant at temperatures above about 150.degree. C. See, e.g., U.S. Pat. No. 3,476,774. Such thermal decomposition in accompanied by evolution of water vapor and oxides of carbon, in a closed reaction vessel, is accompanied by an increase in internal pressure. Under some observed conditions the thermal decomposition can be so rapid as to be explosive. In the absence of explosive thermal decomposition a carbon containing tarry residue is also formed in addition to water vapor and oxides of carbon. Such residue is due to the fact that the anhydrides can react with the water to form the dicarboxylic acids and then isomerize to the trans form (which is insoluble in the system) or to polymerize. Such thermal decomposition and attendant isomerization or polymerization of the unsaturated anhydride reactant has been observed as occurring during its addition reaction with polymeric olefins, e.g. polybutenes and others, in a closed reaction vessel. The carbon-containing residue varies in nature from somewhat granular when the decomposition is only slight to a tarry material mainly adhering to internal surfaces of the reaction vessel when the decomposition is more extensive but well below explosive magnitude. The granular type residue amounts to from about 0.1 to about 0.3 weight percent of the total charge and is generally dispersed in the alkenyl-substituted saturated anhydride addition compound product diluted with unreacted components of the olefin polymer, and is readily separated therefrom by filtration. However, the tarry residual product, which for the most part fouls the internals of the reaction vessel can be as high as 2-3 weight percent of the total charge. The tarry material not adhering to the internal surfaces of the reactor fouls the filter and interferes with filtration of the desired reaction product. Both types of residue are undesirable because of the above noted fouling characteristics and because their formation results in yield reduction of the desired alkenyl-substituted anhydride addition product.
The patent literature discloses a number of compositions and methods which improve yield in the reaction of unsaturated dicarboxylic acid anhydrides (e.g. maleic anhydride), and propene or butene polymers by inhibiting the formation of tarry residual material and undesirable reaction side products which occur because of the above-described thermal decomposition and attendant isomerization or polymerization of the anhydride reactant.
For example, Powell U.S. Pat. No. 4,414,397 discloses reaction of maleic anhydride and polyisobutylene in the presence of 1,3-dibromo-5,5-dialkylhydantoin wherein the rate of addition of the maleic anhydride to the reaction mixture is controlled such that the anhydride is present in an amount less than about its maximum solubility in the reaction mixture in order to maintain the reaction mixture as a substantially homogeneous single phase system. The controlled anhydride addition stems from the patentee's conclusion that presence of a two phase system containing undissolved anhydride "is correlative with production of undesirable sludge or tar with resulting lower yield of desired product" (column 3, lines 7-19). The patent discloses several embodiments for achieving the desired controlled addition of maleic anhydride such as by the addition of equal or varying aliquots of the anhydride over the course of the reaction (column 4, lines 13-57).
Powell U.S. Pat Nos. 4,496,746 and 4,434,071 are also directed to reducing by-product formation in the reaction of maleic anhydride with polyisobutylene. The '071 patent discloses, as a catalyst, a complex of polyisobutylene and a 1,3-dibromo dialkylhydantoin which is stated to reduce by-product formation. The '746 patent discloses addition of maleic anhydride in the form of a dispersion or emulsion in a carrier fluid to minimize sludge formation. At column 5, lines 16-23 of the '746 patent it is stated:
"In the preferred embodiment, the olefin oligomer is added to the reaction vessel and the dispersion of the maleic anhydride is added thereafter. Although it is possible to add the dispersion to the reaction mixture in one aliquot, it is preferred to add it to the reaction mixture in one aliquot, it is preferred to add it to the reaction mixture gradually over the course of the reaction. When catalyst is employed [such as a brominated dialkylhydantoin referred to at column 4 line 33] it may be added with the oligomer or with the maleic anhydride or both."
Of additional relevance to the present invention in view of their disclosures of tar and side product suppressing agents are Cengel et al. U.S. Pat. Nos. 3,927,041; 3,935,249; 3,953,475; 3,954,812; 3,960,900; 3,985,672; 4,008,168; and 4,086,251. The '041 and '672 patents disclose 1,3-dibromo-5,5-dialkylhydantoins as tar and side product inhibiting compounds. The '812 and '168 patents disclose halogenated carboxylic or sulfonic acids as tar suppressants. The '900 patents discloses halogenated aliphatic or aromatic hydrocarbons as tar suppressants. The '475 discloses halogenated aliphatic or aromatic carbonyls for tar and by-product suppression, and the '249 patent discloses inorganic halogen compounds for tar suppression. The '251 patent discloses all of the above suppressants in a method for preparing polyalkenyl substituted anhydrides where unreacted maleic anhydride is recycled to the reaction mixture.
In addition to the patents mentioned above which address the problem of reduced yields in the reaction of maleic anhydride and polyalkenes due to tar and by-product formation, it is, of course, also possible to increase the yield of the preferred polyisobutenyl succinic anhydride (PIBSA) by simply increasing the mole ratio of anhydride to polybutene in the reaction. However, this approach leads to a lower equivalent weight PIBSA which is undesirable in certain applications.
Although the patents cited above address PIBSA yield improvement without need for increased ratios of maleic anhydride to polybutene in the reaction mixture, there is still need for improvement in the reduction of by-product formation in the preparation of alkenyl substituted anhydrides wherein a tar and side product suppressing agent is used.
A general object of the present invention is therefore to provide an improved method for the manufacture of alkenyl-substituted anhydrides, other objects being evident hereinafter to those skilled in the art.